There's no reason why an 'autosave' cannot be done atomically. The autosave features I know of don't write over the real file they write it to a user specified location, the default of which is typically something like %appdata%\somewhere or %documents%\somewhere. Where I can I change it - word, notepad, excel and calibre.
An Autosave will not get you back to the very last keystroke, at best it will get you back to the previously completed autosave - unless of course your autosave device failed. Even Sabre's checkpoint/restart was never 100%, nor was Tandem's Non Stop.
I know of 2 prize winning published authors who turned off autosave in Word (they were told by some geek that it made Windows 'really' slow). They both also lost half or more days work due to power fails - when your on a roll you don't bother with ctrl/s.
BTW when I write something lengthy in Word I don't write it as a monolithic document. I use Word's Master Document feature to break it up into smaller files (parts, chapters), Master Documents first saw the light of day in Word '97. Sound familiar ?
@
AnotherCat - good point, pssst - I filched a Registry patch from Windows 7 Forum that puts gpedit in the control panel.
BR
Sabre is an airline reservations systems - one of first 24*7 transaction processing systems (initially developed in the 1950/60s). Is still used by many (most ?) international airlines ==>> Sabre (computer system)